Optical measurement system and method including blink rate monitor and/or tear film breakup detector

ABSTRACT

An optical measurement system and method measure a characteristic of a subject&#39;s eye. The optical measurement system receives from an operator, via a user interface of the optical measurement instrument, a begin measurement instruction indicating the start of a measurement period for objectively measuring at least one characteristic of the subject&#39;s eye. Subsequent to receiving the begin measurement instruction, the optical measurement system determines whether a criterion associated with the tear film quality of the subject&#39;s eye is not satisfied. In response to determining that the criterion is not satisfied, the optical measurement instrument takes one or more corrective actions to measure the characteristic of the subject&#39;s eye under a condition wherein the criterion is satisfied.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/647,149 filed on 11 Jul. 2017 and issued on 16 Oct. 2018 as U.S. Pat.No. 10,098,534, which is in turn a continuation of U.S. patentapplication Ser. No. 14/789,943 filed on 1 Jul. 2015 and issued on 18Jul. 2017 as U.S. Pat. No. 9,706,912, and claims priority to U.S.Provisional Application No. 62/020,268 filed on 2 Jul. 2014, all ofwhich applications are hereby incorporated by reference in theftentirety.

FIELD OF INVENTION

Embodiments of this invention generally pertain to the field of visiondiagnostics, and particularly to a method and system for objectivelymeasuring an optical characteristic, such as the corneal topography, orrefraction of an eye.

BACKGROUND

Ocular aberrations typically produce unwanted results in the form of badeyesight. To be adequately treatable, these aberrations need to bemeasured and characterized. To this end, various devices, apparatuses,and methods have been developed for objectively measuringcharacteristics, including aberrations, of a subject's eye.

During vision measurements, however, sometimes a subject will stare intothe optical measurement apparatus for an unusually long period of timewithout blinking. When this happens, some individuals will experience adisruption of the tear film on their eye(s). The tear film consists ofthree layers: (1) an outer lipid layer that inhibits evaporation; (2) aninner aqueous layer; and (3) a mucin layer that lies on the cornea. Thecornea repels water, so it is the function of the mucin layer to coatthe cornea, and to provide a hydrophilic layer for the aqueous layer tobe spread over evenly. In particular, if a subject holds her/his eyeopen for too long without blinking, the mucin layer may becomedisrupted. If that happens, it may take several minutes for the mucinlayer to recoat the entire cornea. Until that happens, measurements ofthe eye made during the intervening period will not reflect the eye'snormal optical performance. More specifically, if the corneal topographyand/or refraction of the eye are measured under such a condition whenthe tear film layer has been disrupted, the measurement will includeerrors.

SUMMARY OF THE INVENTION

Therefore, it would be desirable to provide an optical measurementsystem and method which can ensure that measurements are performed whenthe tear film is of an acceptable quality to permit measurements thataccurately conform to the “real world” optical performance of the eye soas to obviate one or more problems due to limitations and disadvantagesof the related art.

In one aspect of the invention, a method is provided for measuring acharacteristic of a subject's eye. The method comprises: an opticalmeasurement instrument receiving from an operator, via a user interfaceof the optical measurement instrument, a begin measurement instructionindicating the start of a measurement period for objectively measuringat least one characteristic of the subject's eye; subsequent toreceiving the begin measurement instruction, determining whether acriterion associated with the tear film quality of the subject's eye isnot satisfied; and in response to determining that the criterion is notsatisfied, taking one or more corrective actions to measure thecharacteristic of the subject's eye under a condition wherein thecriterion is satisfied.

In another aspect of the invention, an optical measurement instrumentcomprises: an optical system configured for objectively measuring atleast one characteristic of a subject's eye; a user interface; and oneor more processors. The one or more processors are configured to receivevia the user interface a begin measurement instruction indicating thestart of a measurement period for objectively measuring at least onecharacteristic of the subject's eye, subsequent to receiving the beginmeasurement instruction to determine whether a criterion associated withthe tear film quality of the subject's eye is satisfied, and in responseto determining that the criterion is not satisfied, to take one or morecorrective actions to measure the characteristic of the subject's eyeunder a condition where the criterion is satisfied.

This summary and the following description are merely exemplary,illustrative, and explanatory, and are not intended to limit, but toprovide further explanation of the invention as claimed. Additionalfeatures, aspects, objects and advantages of embodiments of thisinvention are set forth in the descriptions, drawings, and the claims,and in part, will be apparent from the drawings and detaileddescription, or may be learned by practice. The claims are incorporatedby reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by referring to thefollowing detailed description that sets forth illustrative embodimentsusing principles of the invention, as well as to the accompanyingdrawings of which:

FIG. 1 is a functional block diagram of one embodiment of an opticalmeasurement system.

FIG. 2 is a more detailed diagram of portions of one embodiment of anoptical measurement system.

FIG. 3A and FIG. 3B illustrate a first example embodiment of a progressbar for indicating an elapsed time period associated with the subjectblinking.

FIG. 4A and FIG. 4B illustrate a second example embodiment of a progressbar for indicating an elapsed time period associated with the subjectblinking.

FIG. 5A and FIG. 5B illustrate a third example embodiment of a progressbar for indicating an elapsed time period associated with the subjectblinking.

FIG. 6 illustrates a first example embodiment of a process of insuringthat a tear film quality criterion is satisfied when measuring acharacteristic of a subject's eye.

FIG. 7 illustrates a second example embodiment of a process of insuringthat a tear film quality criterion is satisfied when measuring acharacteristic of a subject's eye.

FIG. 8 illustrates a third example embodiment of a process of insuringthat a tear film quality criterion is satisfied when measuring acharacteristic of a subject's eye.

DETAILED DESCRIPTION

As discussed above, it would be desirable to provide an opticalmeasurement system and method of operation of an optical measurementsystem which can insure that the tear film quality of a subject's eyesatisfies some specified criterion or criteria when measuring one ormore characteristics of the eye. The following description describesvarious embodiments of the present invention. For purposes ofexplanation, specific configurations and details are set forth so as toprovide a thorough understanding of the embodiments. It will also,however, be apparent to one skilled in the art that embodiments of thepresent invention can be practiced without certain specific details.Further, to avoid obscuring the embodiment being described, variouswell-known features may be omitted or simplified in the description.

FIG. 1 is a functional block diagram of one embodiment of an opticalmeasurement instrument or optical measurement system 100 for measuringone or more characteristics of an eye 10. Optical measurement system 100includes a patient interface (e.g., a headrest and eye examinationarea), a camera 120, a corneal topographer 130, a wavefront aberrometer140, one or more displays 150, one or more processors 160 and associatedstorage (e.g., memory) 170, and one or more operator input devices 180for receiving input or instructions from an operator 20. It should beunderstood that optical measurement system 100 is simply one embodimentfor illustrating principles of the invention, and that many variationsare possible which may omit certain elements, add additional elements,and/or change some of the elements. For example, another opticalmeasurement system incorporating one or more aspects of this inventionmay omit conical topographer 130 or wavefront aberrometer 140. Anotheroptical measurement system may include only an autorefractor as ameasurement instrument. Some implementations may include additionalelements, for example one or more loudspeakers.

In some implementations, camera 120 may be an eye alignment camera whichis used to insure proper eye alignment when making corneal topographyand/or wavefront aberrometry measurements with conical topographer 130and/or wavefront aberrometer 140. In some implementations, camera 120may be a separate camera which may be employed to determine when thesubject blinks eye 10, for example in conjunction with a patternrecognition algorithm executed by processor(s) 160, as will be describedin greater detail below. Beneficially, camera 120 alone or inconjunction with processor(s) 160 may provide a continuous live displayof eye 10 to operator 20 via display 150.

Although example configurations of corneal topographer 130 and wavefrontaberrometer 140 will be described in further detail below with respectto FIG. 2, it should be understood that these elements may employ any ofa variety of other configurations.

Display(s) 150 may include one or more display devices which provideimages and/or data to operator 20 under control of processor(s) 160.Such images and data may include operating instructions and/or requestsfor input from operator 20, images of eye 20 produced by camera 120,images and data reflecting measurements of eye 10 performed by conicaltopographer 130 and/or wavefront aberrometer 140, etc. Display(s) 150may include one or more flat panel displays, including one or moretouchscreens, individual lights (e.g., light emitting diodes), or anyother convenient display device(s).

Processor(s) 160 execute(s) computer-readable instructions forperforming operations of optical measurement system 100. Such operationsmay include adjusting one or more operating parameters of cornealtopographer 130 and/or wavefront aberrometer 140, processing data outputby corneal topographer 130 and/or wavefront aberrometer 140,interpreting and responding to inputs and/or instructions received byoperator input device(s) 180, generating images and/or data for displayby display(s) 150, etc. Processor(s) may perform into operations usinginstructions and/or data stored in associated storage 170. Storage 170may include any combination of volatile memory devices (e.g., randomaccess memory), nonvolatile memory devices (e.g., read only memory,FLASH memory), computer readable media such as hard disk drives, opticaldisks, etc. In particular, storage 170 may store an operating system forprocessor(s) 160 and one or more computer programs which are executed byprocessor(s) 160 during operation of optical measurement system 100. Insome implementations, storage 170 may store computer-readableinstructions which cause processor(s) 160 to execute one or morealgorithms for insuring that the tear film quality of a subject's eyesatisfies some specified criterion or criteria when measuring one ormore characteristics of the eye. In some implementations, storage 170may store computer-readable instructions which cause processor(s) 160 toexecute one or more algorithms described below with respect to FIGS.6-8. In some implementations, storage 170 may store raw data produced bycorneal topographer 130 and/or wavefront aberrometer 140, and/or datafrom corneal topographer 130 and/or wavefront aberrometer 140 which hasbeen processed by processor(s) 160.

Operator input device(s) 180 may include any combination of thefollowing devices: keyboard, touchscreen, touchpad, joystick,pushbuttons, roller ball, mouse, keypad, microphone, etc.

In general, processor(s) 160 operate in conjunction with display(s) 150and operator input device(s) 180 to provide a user interface forreceiving instructions and data from operator 20 and for communicatingwarnings, instructions, and data to operator 20.

FIG. 2 is a more detailed diagram of portions of one embodiment of anoptical measurement instrument or optical measurement system 200. System200 comprises a structure 1100 having a principal surface 1120 with anopening or aperture 1140 therein; a plurality of first (or peripheral)light sources 1200 provided on the principal surface 1120 of thestructure 1100; a plurality of second, or central, light sources 1300(sometimes referred to as “Helmholtz light sources”); a detector array1400; a display 150; a processor 160; operator input devices 180; athird light source 1500 providing a probe beam; a wavefront sensor 1550;and an optical system 1700 disposed along a central axis 1002 passingthrough the opening or aperture 1140 of the structure 1100. Opticalsystem 1700 comprises a quarterwave plate 1710, a first beamsplitter1720, a second beamsplitter 1730, an optical element (e.g., a lens)1740, a third beamsplitter 1760, and a structure including an aperture1780. Beneficially, third light source 1500 includes a lamp 1520, acollimating lens 1540, and light source polarizing beamsplitter 1560.Associated with third light source 1500 and wavefront sensor 1550 in awavefront analysis system 1600 also comprising: a polarizingbeamsplitter 1620; an adjustable telescope 1640 comprising a firstoptical element (e.g., lens) 1642 and a second optical element (e.g.,lens) 1644 and a movable stage or platform 1646; and a dynamic-rangelimiting aperture 1650 for limiting a dynamic range of light provided towavefront sensor 1550. It will be appreciated by those of skill in theart that the lenses 1642, 1644, or any of the other lenses discussedherein, may be replaced or supplemented by another type of converging ordiverging optical element, such as a diffractive optical element.Beneficially, system 200 further comprises a fixation target system1800, comprising light source 1820 and lenses 1840, 1860, and 1880.

As used herein the term “light source” means a source of electromagneticradiation, particularly a source in or near the visible band of theelectromagnetic spectrum, for example, in the infrared, near infrared,or ultraviolet bands of the electromagnetic radiation. As used herein,the term “light” may be extended to mean electromagnetic radiation in ornear the visible band of the electromagnetic spectrum, for example, inthe infrared, near infrared, or ultraviolet bands of the electromagneticradiation.

In one implementation, structure 1100 has the shape of an elongated ovalor “zeppelin” with openings or apertures at either end thereof. Anexample of such a structure is disclosed in Meji'a-Barbosa, cited above,as particularly illustrated in FIG. 4 therein. In some implementations,principal surface 1120 of structure 1100 is concave when viewed from thecornea of eye 10, as illustrated in FIG. 2.

In one implementation where principal surface 1120 is concave, principalsurface 1120 may have the shape of a conical frustum. Alternatively,principal surface 1120 may have a shape of a hemisphere or some otherportion of a sphere, with an opening or aperture therein. Alsoalternatively, principal surface 1120 may have the shape of a modifiedsphere or conical frustum, with a side portion removed. Beneficially,such an arrangement may improve the ergonomics of system 200,particularly the patient interface (element 110 in FIG. 1) by moreeasily allowing structure 1100 to be more closely located to eye 10without being obstructed by the subject's nose. Of course, a variety ofother configurations and shapes for principal surface 1120 are possible.

In the embodiment of FIG. 2, the plurality of first light sources 1200are provided on the principal surface 1120 of structure 1100 so as toilluminate the cornea of eye 10. In one implementation, light sources1220 may comprise individual light generating elements or lamps, such aslight emitting diodes (LEDs) and/or the tips of the individual opticalfibers of a fiber bundle. Alternatively, principal surface 1120 ofstructure 1100 may have a plurality of holes or apertures therein, andone or more backlight lamps, which may include reflectors and/ordiffusers, may be provided for passing lighting through the holes toform the plurality of first light sources 1200 which project light ontothe cornea of eye 10. Other arrangements are possible.

In another implementation, structure 1100 is omitted from system 200,and the first light sources 1200 may be independently suspended (e.g.,as separate optical fibers) to form a group of first light sources 1200arranged around a central axis, the group being separated from the axisby a radial distance defining an aperture in the group (correspondinggenerally to the aperture 1140 in the structure 1100 illustrated in FIG.2).

In one implementation, second light sources 1300 comprise a plurality oflamps, such as LEDs or optical fiber tips. Alternatively, second lightsources 1300 may comprise a plurality of holes or apertures in a surfacethat are illuminated by one or more backlight lamps with reflectorsand/or diffusers.

In one implementation, second light sources 1300 are located off thecentral optical axis 1002 of system 200, and light from second lightsources is directed toward optical element 1740 by third beamsplitter1760. Alternatively, second light sources 1300 may comprise a pluralityof lamps disposed on the structure around the aperture 1780,perpendicular to the optical axis 1002.

Beneficially, each of the second light sources 1300 is locatedapproximately one focal length, f, away from optical element 1740.

Detector array 1400 comprises a plurality of light detecting elementsarranged in a two dimensional array. In one implementation, detectorarray 1400 comprises such a charge-coupled device (CCD), such as may befound in a video camera. However, other arrangements such as a CMOSarray, or another electronic photosensitive device, may be employedinstead. Beneficially, the video output signal(s) of detector array 1400are provided to processor(s) 160 which processes these output signalsaccording to known algorithms to produce corneal topography for eye 10.

Beneficially, lamp 1520 of third light source 1500 is an 840 nm SLD(super luminescent laser diode).

Beneficially, wavefront sensor 1550 may be Shack-Hartmann wavefrontsensor comprising a detector array and a plurality of lenslets forfocusing received light onto its detector array. In that case, thedetector array may be a CCD, a CMOS array, or another electronicphotosensitive device. Embodiments of wavefront sensors which may beemployed in one or more systems described herein are described in U.S.Pat. No. 6,550,917, issued to Neal et al. on Apr. 22, 2003, and U.S.Pat. No. 5,777,719, issued to Williams et al. on Jul. 7, 1998, both ofwhich patents are hereby incorporated herein by reference in theirentirety. However, other wavefront sensors may be employed instead.

Wavefront sensor 1550 outputs signals to processor(s) 160 which use(s)the signals to determine ocular aberrations of eye 10. Beneficially,processor(s) 160 is/are able to better characterize eye 10 byconsidering the corneal topography of eye 10, which may also bedetermined by processor(s) 160 based on outputs of detector array 1400,as explained above.

The configurations and operation of display 150, processor 160, andoperator input devices 180 have been described above with respect toFIG. 1, and will not be repeated.

As shown in FIG. 2, optical measurement system 200 further includes aloudspeaker 190 which may provide audible warnings, instructions and/orother audible feedback to operator 20.

Although not shown in FIG. 2, optical measurement system 200 furtherincludes one or more eye illumination sources and camera 120 forcapturing images of a subject's eye 10.

Further details of various example implementations of opticalmeasurement system 200 may be found in U.S. Pat. No. 7,976,163, which isincorporated herein by reference.

As explained above, any measurements of the eye which are made when thetear film has degraded will not reflect the normal optical performanceof the eye. More specifically, if the corneal topography and/orrefraction of the eye are measured under such a condition where the tearlayer has been disrupted, the measurements will be in error.

Accordingly, optical measurement systems 100 and 200 execute one or morealgorithms to insure that the that the tear film quality of a subject'seye 10 satisfies some specified criterion or criteria when measuring oneor more characteristics of eye 10. An explanation of various embodimentsof such algorithms will be described now with respect to opticalmeasurement system 100, but it should be understood that thesedescriptions also may be applied to optical measurement system 200.

In some implementations, optical measurement system 100 receives fromoperator 20, via the user interface (e.g., operator input devices 180)of optical measurement system 100, a begin measurement instructionindicating the start of a measurement period for objectively measuringat least one characteristic of the subject's eye 10. Subsequent toreceiving the begin measurement instruction, optical measurement system100 determines whether or not a criterion or criteria associated withthe tear film quality of the subject's eye 10 is/are satisfied. Inresponse to determining that the criterion/criteria is/are notsatisfied, optical measurement system 100 takes one or more correctiveactions so as to measure the characteristic of the subject's eye 10under conditions where the criterion/criteria is/are satisfied.

In some implementations, optical measurement system 100 may determinethe tear film quality of the subject's eye 10 directly. In suchimplementations, processor(s) 160 may analyze wavefront data output fromwavefront aberrometer 140 to determine that the tear film quality is notwithin acceptable parameters, and in that case may take one or morecorrective actions (e.g., prompt operator 20 to instruct the subject toblink) and then recommence the wavefront measurement(s). For example,when light spots on the detector of wavefront aberrometer 140 do notconform to expected standards, for example due to missing light spots orlight spots which are too large, etc., optical measurement system 100may determine that the tear film quality is not within acceptableparameters. In some implementations, optical measurement system 100 maydetermine the thinness of the tear film and/or a breakup of the tearfilm and use one or both of these as criteria for evaluating the tearfilm quality of a subject's eye 10. For example, in some implementationsoptical measurement system may specify a quality threshold for the tearfilm based on the thinness of the tear films and/or an amount of tearfilm break-up which is detected, and may take one or more correctiveactions as described below when the tear film quality does not meet orexceed the specified quality threshold Processor(s) 160 may employ anyof a variety of analysis algorithms and associated criteria to make thedetermination of tear film quality.

The inventors have appreciated that the tear film quality of a subject'seye 10 may be related to the time interval between blinks of eye 10. Theinventors have further appreciated that tear film can generally beassumed to be stable and of sufficient quality to make accurate eyemeasurements when a subject blinks eye 10 within a “normal” timeinterval, and that after such a normal time interval the tear film maybreak up for some people. For example, eight seconds may be consideredto be a “normal” time interval, and the tear film quality can be assumedto be of acceptable quality any time within eight seconds of the lasttime the subject blinked. On the other hand, about 50% of subjects willhave the tear film start to break up if blinks are more than 12 secondsapart. Also, a typical blink rate for normal visual conditions is about12 blinks per minute, which decreases to about five blinks per minutewhen a person is reading. Many people will complain of eye discomfort ifthe time between blinks exceeds 10-12 seconds. It should be understoodthat the “normal” time interval is a statistical value for a largenumber of subjects, and what may be normal for any particular subject,and what blink rates lead to tear film degradation for any particularsubject, may vary substantially from these numbers.

Accordingly, in some implementations, optical measurement system 100 maydetermine whether or not a criterion or criteria associated with thetear film quality of the subject's eye 10 is/are satisfied bydetermining whether an elapsed time period associated with the subjectblinking exceeds a threshold, and, in response to determining that theelapsed time period associated with the subject blinking exceeds thethreshold, take one or more corrective actions. For example, opticalmeasurement system 100 may determine a time interval from the time whenthe measurements were begun and/or the last time when the subjectblinked eye 10, and when that time interval exceeds a threshold (e.g., 8seconds or 12 seconds), optical measurement system 100 may provide anindication to operator 20 that the subject should blink eye 10.

In some implementations, optical measurement system 100 may determinewhen a subject blinks eye 10 by receiving an input from operator 20 viathe user interface indicating that the subject blinked eye 10.

In some implementations, optical measurement system 100 may determinewhen a subject blinks eye 10 by capturing a series of images of thesubject's eye 10, detecting from the captured images a blink of thesubject's eye 10. In some implementations, processor(s) 160 may employpattern recognition software to detect when the subject's eye 10 blinks.In some implementations, processor(s) 160 may execute an algorithmsimilar to algorithms employed by automatic drowsy-driver detectionsystems which detect eye blinks by vehicle drivers to determine when thedriver has fallen asleep or is no longer awake. An example of such analgorithm is described in “Drowsy Detection On Eye Blink Duration UsingAlgorithm,” Mandeep Singh et al., INTERNATIONAL JOURNAL OF EMERGINGTECHNOLOGY AND ADVANCED ENGINEERING, Vol. 2, No. 4, April 2012.

In some implementations, the series of images of the subject's eye 20are captured by camera 120 and camera 120 is an eye alignment camera ofoptical measurement system 100. In other implementations, camera 120 isa second camera of optical measurement system 100 separate from an eyealignment camera of optical measurement system 100. In that case, camera120 may have a wider field of view and/or a longer depth of field thanthe eye alignment camera.

In some implementations, optical measurement system 100 may provide anindication or instruction to operator 20 via the interface that theoperator should ask the user to blink before commencing measurements. Inresponse to the indication via the user interface to the operator 20that the subject should blink, operator 20 may instruct the subject toblink, and then provide an instruction to optical measurement system 100to begin the measurement of one or more characteristics of eye 10 (forexample, by clicking on a “start measurement” button displayed ondisplay 150). Optical measurement system 100 may start a timer (e.g., atimer of processor(s) 160) to measure an elapsed time interval from thestart time when the “begin measurement” instruction is received fromuser 20 via the user interface.

When the time interval exceeds a defined threshold maximum time interval(e.g., 8 seconds or 12 seconds), then optical measurement system 100 maytake one or more corrective actions. These corrective actions mayinclude stopping further measurements until the tear film quality isdetermined to have improved to an acceptable level, discarding anymeasurements made when the time interval between blinks has beenexceeded and only retain and process measurements made within thedefined threshold maximum time interval, and/or providing an indicationto operator 20 via the user interface that the subject should blink.

In some implementations, after providing an indication to operator 20via the user interface that the subject should blink, opticalmeasurement system 100 may restart or reset the time interval betweenblinks after either detecting a blink automatically via camera 120 andprocessor(s) 160, as described above, or in response to an inputreceived from operator 20 via the user interface indicating that thesubject has blinked.

In some implementations, optical measurement system 100, andparticularly processor(s) 160, may employ a combination of the blinkdetection algorithms described above and/or the tear film qualitydetection algorithms described above to determine whether or not thetear film quality of the subject's eye 10 satisfies the specifiedcriterion or criteria when measuring one or more characteristics of eye10. When the tear film quality does not satisfy the specified criterionor criteria, then optical measurement system 100, and particularlyprocessor(s) 160, may take one or more corrective actions as describedabove, including stopping further measurements until the tear filmquality is determined to have improved to an acceptable level,discarding any measurements made when the tear film quality isunacceptable and only retain and process measurements made within thetear film quality is deemed acceptable, and/or providing an indicationto operator 20 via the user interface that the subject should blink. Insome implementations, processor (s) 160 of optical measurement system100 may store eye blink data or an eye blink record in storage 170 whichincludes a record of the history of the subject's blinks of eye 10during the time when measurements of eye are made. In someimplementations, the eye blink data or record may be associated instorage 170 with the corresponding data produced by optical measurementsystem 100 from the measurements of eye 10. For example a patient recordfor a subject may be stored in storage 170 and include the objectivemeasurement data, measurement conditions (e.g., measurement date,operator, etc.), one or more eye images, the blink history, personalidentification data, and other relevant data pertaining to the subject,etc.

In some implementations, the indication to operator 20 that the subjectshould blink may be provided as a text message on display 150.

In some implementations, the indication to operator 20 that the subjectshould blink may be provided as an audible signal via a loudspeaker.

In some implementations, the indication to operator 20 that the subjectshould blink is provided via a progress bar displayed on a display 150of optical measurement system 100. In that case, the progress bar isreset to zero when optical measurement system 100 determines that thesubject blinks, as explained above.

FIG. 3A and FIG. 3B illustrate a first example embodiment of a progressbar 310 for indicating to user 20 an elapsed time period associated withthe subject blinking. Progress bar 310 displays a percentage from 0% to100% based on the relationship between the time interval from the lasttime that the subject blinked and a specified maximum time intervalbetween blinks which is set by software of optical measurement system100. In some implementations, the specified maximum time intervalbetween blinks may be between 8 and 12 seconds. For example, in someimplementations, the specified maximum time interval between blinks maybe 8 seconds. In other implementations, the specified maximum timeinterval between blinks may be 12 seconds. However, it should beunderstood that other specified maximum time interval between blinks maybe employed, and that the specified maximum time interval between blinksmay be varied from subject to subject. In some implementations, onceprogress bar 310 reached 100%, its color may change (from example, fromgreen to red) and/or it may begin to blink to draw the attention ofoperator 20.

Here, progress bar 310 is displayed horizontally, but of course it couldbe displayed vertically.

In response to detecting a blink of subject's eye 10, opticalmeasurement system 100 restarts the time interval for measuring when thesubject last blinked, as described above, and resets progress bar 310back to 0%.

FIG. 4A and FIG. 4B illustrate a second example embodiment of a progressbar 410 for indicating an elapsed time period associated with thesubject blinking. Here, a first portion (e.g., a first third) ofprogress bar 410 is displayed in a first color (e.g., green), a secondportion (e.g., a second third) of progress bar 410 is displayed in asecond color (e.g., yellow), and a third portion (e.g., a last third) ofprogress bar 410 is displayed in a third color (e.g., color).

Progress bar 410 may represent a specified maximum time interval betweenblinks which is set by software of optical measurement system 100. Insome implementations, the specified maximum time interval between blinksmay be between 8 and 12 seconds. For example, in some implementations,the specified maximum time interval between blinks may be 8 seconds. Inother implementations, the specified maximum time interval betweenblinks may be 12 seconds. In some implementations, once progress bar 410has reached its end, the color of one or all of the segments may change(from example, to all red) and/or it may begin to blink to draw theattention of operator 20.

Here, progress bar 410 is displayed horizontally, but of course it couldbe displayed vertically.

In response to detecting a blink of subject's eye 10, opticalmeasurement system 100 restarts the time interval for measuring when thesubject last blinked, as described above, and resets progress bar 410back to the beginning.

FIG. 5A and FIG. 5B illustrate a third example embodiment of a progressbar 610 for indicating an elapsed time period associated with thesubject blinking. Here, optical measurement system 100 includes a firstdisplay 150-1 and a second display 150-2 which comprises a group ofindividual light elements (e.g., light emitting diodes (LEDs)). Here,second display 150-2 comprises ten LEDs arranged horizontally, but ofcourse any number of LEDs may be included, and the LEDs could bearranged vertically. Progress bar 610 is displayed via second display150-2. In this example, the first four LEDs are green, the next threeLEDs are yellow, and the last three LEDs are red. Again, any combinationof colored elements may be employed.

Progress bar 510 may represent a specified maximum time interval betweenblinks which is set by software of optical measurement system 100. Insome implementations, the specified maximum time interval between blinksmay be between 8 and 12 seconds. For example, in some implementations,the specified maximum time interval between blinks may be 8 seconds. Inother implementations, the specified maximum time interval betweenblinks may be 12 seconds. In this example where there are ten LEDs, eachLED may represent 10% of the specified maximum time interval betweenblinks. In that case, another LED may be illuminated every time that thetime interval reaches another 10% of the specified maximum timeinterval, until all ten LEDs are illuminated, or until the time intervalis reset by the subject blinking. In some implementations, once progressbar 510 has reached its end, the color of one or all of the elements maychange (from example, to all red) and/or the elements begin to blink todraw the attention of operator 20.

In response to detecting a blink of subject's eye 10, opticalmeasurement system 100 restarts the time interval for measuring when thesubject last blinked, as described above, and resets progress bar 510back to the beginning, turning off all of the LEDs.

FIGS. 3-5 illustrate a few example embodiments of progress bar foroptical measurement system 100 which may have certain beneficialfeatures, but it should be understood that in general a progress barhaving any desired configuration may be employed.

In some implementations, the indication to operator 20 that the subjectshould blink may be provided by various combinations of the textmessage, progress bar, and audible signals described above.

In some cases, it is possible that the tear film may be degraded due tothe subject holding eye 10 open too long while staring into opticalmeasurement system 100, leading to excessive watering of eye 10. In thatcase, in some implementations optical measurement system 100 may employa tear film quality criterion which includes determining whether thesubject's eye exhibits excessive tearing. For example, in someimplementations excessive tearing may be detected by pattern recognitionof shimmering reflections of the eye illumination light source(s) asseen by camera 120. In that case, a corrective action taken by opticalmeasurement system 100 in response to determining that the subject's eyeexhibits excessive tearing, may be to delay objective measurement of thecharacteristic(s) of the subject's eye 10 by a specified delay period(e.g., two or three seconds) to allow the tearing to dissipate. Anothercorrective action may be to discard any measurements made when there isexcessive tearing, and only retain and process measurements when thetear film quality is acceptable.

FIG. 6 illustrates a first example embodiment of a method or process 600of insuring that the tear film quality criterion is satisfied whenmeasuring a characteristic of a subject's eye. In some implementations,optical measurement systems 100 and/or 200 may employ process 600.

Process 600 includes an operation 610. In operation 610, the opticalmeasurement system receives from a user via a user interface a BeginMeasurement instruction indicating the start of a measurement period forobjectively measuring at least one characteristic of a subject's eye.

In operation 620, the optical measurement instrument determines whetherone or more criterion associated with the tear film quality of thesubject's eye is satisfied. If the criterion/criteria is/are satisfied,then the process proceeds to operation 630. Otherwise, the processproceeds to operation 640.

In operation 630, the optical measurement system continues toobjectively measure one or more characteristics of the subject's eye(e.g., via corneal topography and/or wavefront aberrometry). As themeasurement(s) proceed(s), operation 620 is repeated.

In operation 640, the optical measurement system takes one or morecorrective actions to measure the characteristic(s) of the subject's eyeunder a condition wherein the criterion or criteria are satisfied. Thecorrective actions may include stopping further measurements until thetear film quality is determined to have improved to an acceptable level,and/or providing an indication to the operator of the opticalmeasurement system via the user interface that the subject should blink.

FIG. 7 illustrates a second example embodiment of a method or process700 of insuring that a tear film quality criterion is satisfied whenmeasuring a characteristic of a subject's eye. In some implementations,optical measurement systems 100 and/or 200 may employ process 700.

Process 700 includes an operation 710. In operation 710, the opticalmeasurement system receives from a user via a user interface a BeginMeasurement instruction indicating the start of a measurement period forobjectively measuring at least one characteristic of a subject's eye.

In operation 720, the optical measurement instrument determines whetheran elapsed time period associated with the subject blinking is less thana defined threshold. For example, in some implementations, the opticalmeasurement instrument determines whether a time interval measured fromthe last time that the subject blinks is less than a specified maximumtime interval between blinks. If the criterion/criteria is/aresatisfied, then the process proceeds to operation 730. Otherwise, theprocess proceeds to operation 740.

In operation 730, the optical measurement system continues toobjectively measure one or more characteristics of the subject's eye(e.g., via corneal topography and/or wavefront aberrometry). As themeasurement(s) proceed(s), operation 720 is repeated.

In operation 740, the optical measurement system provides an indicationto the operator of the optical measurement system via the user interfacethat the subject should blink.

FIG. 8 illustrates a third example embodiment of a method or process 800of insuring that a tear film quality criterion is satisfied whenmeasuring a characteristic of a subject's eye. In some implementations,optical measurement systems 100 and/or 200 may employ process 800.

Process 800 includes an operation 810. In operation 810, the opticalmeasurement system receives from a user via a user interface a BeginMeasurement instruction indicating the start of a measurement period forobjectively measuring at least one characteristic of a subject's eye.

In operation 820, the optical measurement system detects the tear filmquality for the subject's eye. As explained above, in variousimplementations this may include determining the thinness of the tearfilm and/or an amount of percentage of breakup of the tear film.

In operation 830, the optical measurement instrument determines whetheror not the tear film quality of the subject's eye meets a specifiedquality threshold. If the specified quality threshold is met orexceeded, then the process proceeds to operation 840. Otherwise, theprocess proceeds to operation 850.

In operation 840, the optical measurement system continues toobjectively measure one or more characteristics of the subject's eye(e.g., via corneal topography and/or wavefront aberrometry). As themeasurement(s) proceed(s), operation 620 is repeated.

In operation 850, the optical measurement system takes one or morecorrective actions to measure the characteristic(s) of the subject's eyeunder a condition wherein the criterion or criteria are satisfied. Thecorrective actions may include stopping further measurements until thetear film quality is determined to have improved to an acceptable level,and/or providing an indication to the operator of the opticalmeasurement system via the user interface that the subject should blink.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. The term “connected” is to beconstrued as partly or wholly contained within, attached to, or joinedtogether, even if there is something intervening. Recitation of rangesof values herein are merely intended to serve as a shorthand method ofreferring individually to each separate value falling within the range,unless otherwise indicated herein, and each separate value isincorporated into the specification as if it were individually recitedherein. All methods described herein can be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or exemplarylanguage (e.g., “such as”) provided herein, is intended merely to betterilluminate embodiments of the invention and does not pose a limitationon the scope of the invention unless otherwise claimed. No language inthe specification should be construed as indicating any non-claimedelement as essential to the practice of the invention.

Other variations are within the concept, scope, or spirit of the presentinvention. While the invention is susceptible to various modificationsand alternative constructions, certain illustrated embodiments of theinvention are shown in the drawings, and have been described above in anexemplary form with a certain degree of particularly. Those of ordinaryskill in the art will understand, however, that the embodiments areprovided by way of example only, and that various variations can be madewithout departing from the spirit or scope of the invention. Thus, thereis no intention to limit the invention to the specific form or formsdisclosed. Rather, it is intended that this disclosure cover allmodifications, alternative constructions, changes, substitutions,variations, as well as the combinations and arrangements of parts,structures, and steps that come within the spirit and scope of theinvention as generally expressed by the following claims and theirequivalents.

We claim:
 1. A method for measuring a characteristic of a subject's eye,the method comprising: an optical measurement instrument receiving froman operator, via a user interface of the optical measurement instrument,a begin measurement instruction indicating the start of a measurementperiod for objectively measuring at least one characteristic of thesubject's eye; subsequent to receiving the begin measurementinstruction, determining whether the subject's eye exhibits excessivetearing; and in response to determining that the subject's eye exhibitsexcessive tearing, taking one or more corrective actions to measure thecharacteristic of the subject's eye under a condition wherein thesubject's eye does not exhibit excessive tearing.
 2. The method of claim1, wherein the one or more corrective actions includes discarding anymeasurements made when there is excessive tearing.
 3. The method ofclaim 1, wherein determining whether the subject's eye exhibitsexcessive tearing includes: capturing a series of images of thesubject's eye, and employing pattern recognition to detect in thecaptured images shimmering reflections of light sources by the eye; anddetermining that the subject's eye exhibits excessive tearing based onthe detected shimmering reflections.
 4. The method of claim 3, whereinthe series of images of the subject's eye are captured by an eyealignment camera of the optical measurement instrument.
 5. The method ofclaim 3, wherein the series of images of the subject's eye are capturedby a second camera of the optical measurement instrument separate froman eye alignment camera of the optical measurement instrument, whereinthe second camera has a wider field of view and longer depth of fieldthan the eye alignment camera.
 6. The method of claim 1, wherein thecharacteristic of the subject's eye includes a wavefront aberration ofthe eye.
 7. The method of claim 1, wherein the characteristic of thesubject's eye includes a corneal topography of the eye.
 8. An opticalmeasurement instrument, comprising: an optical system configured forobjectively measuring at least one characteristic of a subject's eye; auser interface; and one or more processors, the one or more processorsbeing configured to receive via the user interface a begin measurementinstruction indicating the start of a measurement period for objectivelymeasuring at least one characteristic of the subject's eye, subsequentto receiving the begin measurement instruction to determine whether thesubject's eye exhibits excessive tearing, and in response to determiningthat the subject's eye exhibits excessive tearing, to take one or morecorrective actions to measure the characteristic of the subject's eyeunder a condition where the subject's eye does not exhibit excessivetearing.
 9. The optical measurement instrument of claim 8, wherein theone or more corrective actions includes the one or more processorsdiscarding any measurements made when there is excessive tearing inmeasuring the characteristic of the subject's eye.
 10. The opticalmeasurement instrument of claim 8, further comprising a first cameraconfigured to capture a series of images of the subject's eye, andwherein the one or more processors are further configured to employpattern recognition to detect in the captured images shimmeringreflections of light sources by the eye, and wherein the one or moreprocessors are further configured to determine that the subject's eyeexhibits excessive tearing based on the detected shimmering reflections.11. The optical measurement instrument of claim 10, wherein the firstcamera is an eye alignment camera.
 12. The optical measurementinstrument of claim 10, further comprising a second camera which is aneye alignment camera, wherein the first camera has a wider field of viewand longer depth of field than the eye alignment camera.
 13. The opticalmeasurement instrument of claim 8, further comprising a wavefrontaberrometer, wherein the characteristic of the subject's eye includes awavefront aberration of the eye.
 14. The optical measurement instrumentof claim 8, further comprising a corneal topographer, wherein thecharacteristic of the subject's eye includes a corneal topography of theeye.